530 PATHOGENIC MICROORGANISMS 



and para-types, and a considerable number of intermediates, if pos- 

 sible, to represent individuals from various parts of what we may 

 call the spectrum of intermediate agglutination types. The choice 

 of cultures is perhaps the most important single feature in serum 

 production, and those who undertake to produce serum should be 

 constantly receiving cultures from various parts of the country, 

 isolated from cases, checking them up with their serum product, 

 and adding them to their immunizing collection, if they are not 

 represented by antibodies in the polyvalent serum. It is still a 

 question of demanding some research, whether or not a definite 

 limitation of the number of strains used for immunization would 

 be of advantage, since the use of too many different strains may 

 keep down the agglutination value of the serum of the immunized 

 horse. The cultures injected into the horse are grown on agar, 

 and once washed in salt solution before injection. Various routines 

 for the injection of horses have been devised, the most useful method 

 at the present time consisting of injecting on two or three consecu- 

 tive days, giving rests of seven or eight days, between courses of 

 injection. By this method, antibody production may be speeded up. 

 It is unnecessary here, however, to go into the details of the actual 

 technical procedures and measurements used in the production of 

 serum. These methods are constantly changed and can be learned 

 only by taking part in the process in a well equipped producing 

 laboratory. 



Serum must be standardized before it can be marketed. This 

 has been a very difficult matter and a number of suggestions have 

 been made. Flexner and Jobling 39 first attempted standardization 

 by opsonin contents. Complement fixation has been recommended 

 by some writers, but the usual method at the present time is that 

 of agglutination. As a general rule Flexner states that the poly- 

 valent sera are ready for use when they agglutinate the normal 

 and para-types in dilutions of 1 :1500 or 1 :2000. Such sera should 

 also agglutinate intermediate strains in dilutions of 1 :200 and 

 upward. 



Administration of Serum. The most important single considera- 

 tion in serum treatment of meningitis is the early recognition of 

 the case and avoidance of delay in starting the specific treatment. 

 Failure of serum treatment can probably in most cases be referred 



89 Flexner and Jobling, Jour. Exper. Med., 10, 1908. 



